The
situation when a negative lens is used to form an image is simpler than for a
positive lens, because the general features of the image are the same no matter
where the object is located.
The
green ray, which strikes the lens parallel to the axis emerges on the other
side of the lens as if it had originated at the focal point a shown.
The
blue ray, which strikes the lens at its center, emerges on the other side
without any change in its direction.
The
purple ray, which strikes the lens in a direction that is headed for the focal
point on the opposite side of the lens, emerges on the other side parallel to
the axis.
These
rays do not converge to an image. Rather, they appear to come from a virtual image
which is smaller than the object, has the same orientation as the object, and
is located between the lens and the focal point as shown in the figure.